Ok, so I have a new starter, new battery, new solenoid, and all grounds are firm and good, the battery neg to the car chassis. Ground from the engine to the chassis, and I even wire brushed behind the solenoid and voltage regulator. The meter reads 12 volts coming in to the solenoid, 12volts from the ignition terminal, however the cable to the starter while cranking is only getting 6 volts, also the starter switch from the neutral safety switch is reading 6 volts... The starter hits, turns the fly wheel one notch and when I come off the key, I hear the starter retract.. Anyone have an idea what's my cars problem? I have bypassed the netrual switch and the same thing happens... I am so lost... The mustang was a basic grande, however the car now has a 351c from a 72 Torino ... Pretty this doesn't matter as the cars wiring is OEM...

 

The battery negative should go straight to the block, not the chassis. Then from the block to the chassis. The starter grounds agains the block, so you need your battery grounded there as well.

 

The battery is located in the trunk, 0 gauge power wire from positive terminal to the solenoid. 0 gauge neg cable 24 in to the chassis in the rear, 10 inch of 0 gauge from the chassis to the block in the front. I can put the multimeter to a hot wire and ground on anything the isn't painted and get a good circuit, the neg cable/grounds are good? I have no dimming of lights, not even during cranking, when I am getting 6 volts on the starter.... Could the "new" solenoid be defective? Or could it be the ignition switch inside the steering column?

Also, would it be of note that I recently had the motor out and replaced the battery panel under the hood on the passenger side of the care where the solenoid mounts, could the welding of the panel have messed up something? Again lost...

 

Just for troubleshooting, ground the frame of the solenoid to the block using a temporary jumper wire. That will tell you if it is the ground on the solenoid. If it is not the ground on the solenoid it is most likely bad. And yes new parts can be bad.

 

Outta town at the moment, I will try that on Monday and pick up another solenoid if it's the culprit.. Will post the results Monday... Thanks for the input..

 

I'd start with using the negative battery post for the voltmeter minus connection (not the battery cable clamp, hold the meter lead on the post itself).
Take readings with the positive meter lead on both sides of the solenoid (not at the same time), engine block, the starter plus and starter case. You should see the prob pretty easily. If you post the reading here, we'll let you know where the problem is.

 

if the problem sticks around after checking the solenoid, I will move the battery back up front and run the checks no repost...

 

I mean to say run the checks and repost

 

Ok, so I replaced the solenoid, metered 12 volts at the battery side, 12 volts at the "I" terminal in run position. 6.5 volts at the "s" terminal when cranking, 6.5 volts at the starter side of the solenoid. I took the cable off the starter and metered the cable to the chassis ground and cranked and got a full 12 volts, thus I figured I needed to ground the starter/transmission, so I installed a 2gauge ground cable with copper fittings from the lower starter retaing bolt to the chassis ground... And again still getting 6.5 volts at the "s" terminal and at the starter power terminal itself.

 

The Mustang does not have a real frame. It is a sheet metal fold up and as such is a very poor conductor. You need a wire ground from the battery to the engine block. The solenoid is just a large set of contacts, that when new has very little resistance. So if the large wire does not work, suspect that the new starter is bad.